Are Dark Gums Sings Of Infection And Bad Oral Hygiene?

I have seen a lot of people of colour with very dark gums and these same people happen to have very white teeth. My question is: can the darkness be related to some kind of infection? Because I saw an advertisement in which they said the the colour of healthy gums is pink.

In what way is the colour related to the healthiness of your mouth and to the whiteness of the teeth?